Epicyclic Gear Research Articles

Improving Gearbox Design and Analysis for Offshore Wind Turbines

The paper outlines challenges in improving wind turbine availability to reduce the cost of offshore wind energy. It reports the development of a design software tool for wind turbine gearboxes. It facilitates efficient conceptual designs of wind turbine gearboxes with combinations of epicyclic and parallel gear trains. Field loading conditions are obtained by analysing SCADA (Supervisory Control and Data Acquisition) data to support fatigue damage estimation based on Miner’s rule. Results show that considerable overloading conditions are present which would result in significant fatigue damages to the gearbox.

Study on Visualization of Planetary Gear Based on Topological Theory

Analyzed the topological graph based on the methods of functional fractionation, the new topological graph was established on this basis, the new graph’s exact information then can be obtained by computer. By using the software of visual basic 6.0, developed a human-computer interaction interface. The interface achieved three functions: first, we can draw the topological graph through the interface. Second, achieved the function of extract the graph’s information, finally realized the function of automatic assembly the epicyclic gear trains based on the extracted information. In order to meet the requirement of innovative design and parametric design, the author developed the part model library. At last, an example of automatic planetary gear assembly was given.

Tribological optimization of a toroidal-type continuously variable transmission

Continuously variable transmissions (CVTs) are mechanical devices that allow a continuous variation of the output velocity by adjusting its internal geometrical configuration. Through the use of an epicyclic gear set, a CVT can deliver an infinite number of transmission ratios, allowing the vehicle's engine to operate within a higher efficiency envelope for longer periods of time. This offers several advantages over traditional transmissions such as better fuel efficiency, quieter operation, and a lower mass. Current efforts to reduce the vehicles’ fuel consumption in order to protect the environment and save fuel have seen a recent revival in CVT research, especially in the automotive industry. This article documents a successfully implemented search algorithm for the dimensional optimization of a novel CVT design in order to determine the maximum theoretical efficiency of the device. In addition to showing an economical and simple method of calculating contact losses, this method of optimization also proved to be a powerful tool that can be used to select the dimensions of the transmission to fulfil any desired characteristics.

The Instantaneous Efficiency of Epicyclic Gears in Flight Control Systems

The instantaneous efficiency of an epicyclic gear rotary actuator is an important factor in sizing flight control systems where compound epicyclic gear trains are typically used. The efficiency variation can be smooth or fluctuating depending on the combination and timing of the teeth of ring, planet, and sun gears. In this paper, the instantaneous efficiency characteristics of synchronous and nonsynchronous actuators under forward-driving with opposing load and reverse-driving with aiding load are investigated. The emphasis will be on instantaneous, rather than average efficiency of gears. Several gear arrangements are considered: external and internal gears, simple planetary gears and compound planetary gears. Efficiency will be discussed considering not only the geometry of the mating gears, but also the relative phasing of the planet gears relative to the sun and ring gears. Synchronous compound epicyclic gears are shown to have large fluctuation in their instantaneous efficiency. When reverse-driving efficiency falls below 0%, the unit cannot be back-driven and will chatter. Nonsynchronous compound gears have a smaller variation in instantaneous efficiency. However, extra care must be taken in timing the compound planet gears, as well as clocking position of compound planet gears relative to ring gears and the sun gear.

Theoretic Study of Efficiency of Two-DOFs of Epicyclic Gear Transmission via Virtual Power

Epicyclic gear train is a fundamental form of mechanical transmission with broad applications. Efficiency study of these trains is critical to design, optimization, and operation. It is known that the efficiencies of these systems are highly related to the internal power flows. We apply the concept of virtual power to find analytical expression of the efficiency of a two degrees of freedom train, with associated applicable ranges. The results are verified by an example.

Analysis on the Failure Mechanism of Un-Connecting Rod Engine Gear Assembly

With the respect of the phenomenon that gear teeth are broken in the gear-gear ring striking gear of un-connecting rod engine, this paper analyzes its movement rule, and applies the explicit integral finite element method to simulate its dynamics. It shows that the theory engagement of gear-gear ring conforms to the rule of epicyclic gear train, and the deviation of the phase angle caused by mismachining tolerance is the main reason why gear teeth are broken.

Epicyclic Load Sharing Map — Development and validation

Under ideal conditions, every sun–planet–ring path in an epicyclic gear set transmits the same amount of torque. But, in the presence of certain manufacturing variations, equal load sharing is not achieved. In a companion paper, a physical explanation has been provided for the load sharing behavior observed in epicyclic gears. The explanation of the root cause led to the development of a load sharing formulation for 3, 4, 5, and 6 planet epicyclic systems. In this paper the same approach will be taken to develop the formulation for a seven planet epicyclic gear set. The developed expressions will then be used to develop the concept of an Epicyclic Load Sharing Map. This map describes the load sharing characteristics of every epicyclic gear set at any positional error and torque level. The developed expressions are then expanded to describe the general case when there are arbitrary errors on the position of every planet in the epicyclic gear set. Finally, the developed expressions will be validated by comparing the predicted load sharing behavior with the results from a validated system level computational model.

Innovation Synthesis of Basic Configurationof Epicyclic Gear Trains with Three-Degrees of Freedom

Epicyclical gear trains with three-degrees of freedom have found its wide application as the development of new technique. Currently, nearly all domestic researches on epicyclical gear trains with three or more degrees of freedom are aimed at the practical application, and scare works systematically investigate basic configuration and synthesis of the train system. An innovation synthesis method is proposed based on the compound joint kinematic chain and the substitution of low pair with high pair for epicyclical gear trains with three-degrees of freedom, and the possible independent basic configurations of epicyclical gear trains with three-degrees of freedom are obtained by applying the proposed method and the utilization of the method is also discussed. The method provides not only a new approach for innovation synthesis of epicyclical gear trains but also a few basic configurations of epicyclical gear trains with three-degrees of freedom for practice design.

Modelling and simulation of a dual-clutch transmission vehicle to analyse the effect of pump selection on fuel economy

Positive displacement pumps are used in automotive transmissions to provide pressurised fluid to various hydraulic components in the transmission and also lubricate the mechanical components. The output flow of these pumps increases with pump/transmission speed, almost linearly, but the transmission flow requirements often saturate at higher speeds, resulting in excess flow capacity that must be wasted by allowing it to drain back to the sump. This represents a parasitic loss in the transmission leading to a loss in fuel economy. To overcome this issue, variable displacement pumps have been used in the transmission, where the output flow can be reduced by controlling the displacement of the pump. The use of these pumps in automatic transmissions has resulted in better fuel economy as compared with some types of fixed displacement pumps. However, the literature does not fully explore the benefits of variable displacement pumps to a specific type of transmission namely, dual-clutch transmission (DCT), which has different pressure and flow requirements from an epicyclic gear train. This paper presents an analysis of the effect of pump selection on fuel economy in a five-speed DCT of a commercial vehicle. Models of the engine, transmission, and vehicle are developed along with the models of two different types of pumps: a fixed displacement gerotor pump and a variable displacement vane pump. The models are then parameterised using experimental data, and the fuel economy of the vehicle is simulated on a standard driving cycle. The results suggest that the fuel economy benefit obtained by the use of the variable displacement pump in DCTs is comparable to the benefit previously shown for these pumps in automatic transmissions.

Enumeration of Feasible Clutching Sequences of Epicyclic Gear Mechanisms

A new methodology for enumeration of feasible clutching sequences of epicyclic gear mechanism (EGM) composed of two or more fundamental gear entities is presented. The method relies on previous work on algorithmic technique. It improves on existing techniques used for automatic transmission mechanisms in its ability to accurately solve the kinematics of geared mechanisms and estimating their velocity ratios and arranging them in a descending order in a simpler manner without depending on certain gear sizes. Twelve velocity-ratio-relations are derived for any four coaxial links of an epicyclic gear train. These velocity-ratio-relations are three more than the nine relations given in literature. In addition, the velocity ratios can be arranged in a descending sequence without using complicated artificial intelligence technique or complicated computer algorithm. The present methodology is judged to be more efficient for enumeration of all feasible clutching sequences of an EGM.

Method for analyzing epicyclic gearboxes

This paper presents a method for analyzing epicyclic gearboxes by evaluating the speeds, torques and power of the external elements in epicyclic gear mechanisms, as well as the total ratios of the gear box. The method is based on the equations that describe each epicyclic gear mechanism and rules that assign appropriate codes to the external elements. The method emphasizes how power flows are transmitted through the epicyclic gears, as well as power losses. Analysis of an epicyclic gear box is performed to illustrate the proposed method.

Modeling and Simulation of an Inertia-Type Infinitely Variable Transmission

A fully mechanical, infinitely variable transmission (IVT) based on the use of an oscillating inertia is described. The system includes a four-bar linkage mechanism, an epicyclic gear train, and a pair of one-way clutches. The IVT can be used in place of both gearbox and clutch in self-propelled vehicles. A mathematical model is presented. Numerical simulations compare the behavior of a car fitted with a manual gearbox and the same car fitted with the IVT.

Diagnostics practice of heavy duty high speed gear transmissions

Condition monitoring of the gear power transmis-sions teeth meshing vibrations and bearings vibration evaluation are studied in this article. The research results were acquired in practice during long term diagnostics of energy generating machines in situ. The ordinary helical gear train has few times higher vibration acceleration level in comparison with epicyclical gear train. The gears vibra-tion acceleration parameter was used for diagnostics and evaluation teeth meshing quality as high frequency vibra-tion in antifriction bearing diagnostics.

An Approach to Power-Flow and Static Force Analysis in Multi-Input Multi-Output Epicyclic-Type Transmission Trains

This study contributes to the development of a systematic methodology for the torque and power-flow analyses of multi-input multi-output (MIMO) epicyclic gear mechanisms (EGMs) with or without reaction link based on the concept of fundamental circuit. The studies on power-flow analysis of EGMs are mostly done in the context of efficiency formulations. In the opinion of the authors, the design process of the MIMO mechanism involves not only finding the configuration that provides the correct velocity ratios but also meeting other kinematic requirements and ensuring that the two inputs have a mutually constructive nature. To demonstrate the analysis, a new motor/generator integrated hybrid transmission design is used to show how the torque acting on each link of an epicyclic gear train (EGT) can be systematically solved in terms of input torque(s) and/or controlled output torque. This paper presents a unification of kinematic and torque balance approaches for the analysis of MIMO epicyclic-type transmission trains. The results presented are meant to deepen the knowledge as to how and why a MIMO epicyclic-type transmission should operate in a certain way under the given conditions. In the process, this paper explores the theoretical bases of operation of the Toyota Hybrid System and the root cause of some confusion in the field of EGTs.

A Numerical Approach to Calculation of Load Sharing in Planetary Gear Drives

In AGMA 6123-B06 [2006, “Design Manual for Enclosed Epicyclic Gear Drives,” ANSI/AGMA Paper No. 6123-B06], a specific table is given for estimation of the planet load share factor Kγ, as it is termed in that publication; that table is vague as to the exact relationship of tolerance and load to the value of Kγ. Others have done significant works on the subject of load sharing among planets; a brief review of that work is presented. This work calculates a useful value of Kγ directly from design tolerance values and the torque applied to the carrier, and other factors showing how this can be done. This formulation is designed explicitly for nonfloating systems, but may be adaptable to floating systems. The use of flexible planet pins to improve load sharing is discussed. In addition, treating Kγ as a constant with respect to torque for a given planetary design is shown to be inaccurate.

Load sharing behavior in epicyclic gears: Physical explanation and generalized formulation

Abstract In an n planet epicyclic gear set, under ideal conditions, each path will carry an equal amount of torque and therefore can be designed to transmit only 1/ n of the input torque. However, earlier works have shown that such equal sharing of the input torque between the parallel paths is not realized in practical applications, due to the presence of manufacturing errors. While various aspects of the load sharing behaviors have been shown both through computational models and experiments, a physical understanding of the true nature of the load sharing behavior is still lacking. In this paper, a physical explanation will be provided for the basic mechanism causing the unequal load sharing phenomenon. Both floating (system with clearances) and non-floating systems will be treated. On the basis of the physical explanation, closed form non-dimensional equations that predict the planet to planet load sharing behavior in the presence of positional errors will be derived. Epicyclic systems having 3–6 planets will be specifically treated and generalized equations for systems having an arbitrary number of planets will be presented. The developed expressions will be validated by comparing their predictions with previously published predictions from a computational model and experimental data.

Design and fabrication of a statically stable stair‐climbing robotic wheelchair

PurposeThe purpose of this paper is to present the mechanical design and stability analysis of a new stair‐climbing robotic wheelchair.Design/methodology/approachA prototype stair‐climbing robotic wheelchair is constructed comprising a pair of rotational multi‐limbed structures pivotally mounted on opposite sides of a support base. The short arm, long arm, and triangular support structures within each rotational multi‐limbed structure rotate under the actuating effects of epicyclical gear trains.FindingsThe robotic wheelchair ascends and descends stairs in a statically stable manner and has an efficient planar navigation capability.Research limitations/implicationsIn its current state of development, the robotic wheelchair is controlled and powered remotely via umbilical cords rather than an onboard processor and power supply.Practical implicationsThe robotic wheelchair provides an effective solution for enhancing the mobility of the elderly and disabled.Originality/valueThe rotational multi‐limbed mechanisms are developed to ensure the stability of the sitting base at all stages of the stair navigation maneuver without the need for additional servo‐mechanism. The proposed robotic wheelchair shows the simplification of the associated operation process.

Electromechanical drive for rotary mechanisms in spacecraft

It has been shown the advantages of electromechanical drive of angular rotation with torque ac converter-fed motor, epicyclic gear, and with cylinder-conic engagement in comparison with existing drives of the same intention. The block diagram of the drive and of reductor engagement, and also some recommendations of how to calculate it are presented.

The design of spherical multilobe-cam mechanisms

Cam—roller mechanisms can be used in transmissions and robotic devices as an alternative to their bevel-gear counterparts. As bevel gears are used to couple shafts of intersecting axes, their cam-mechanism replacements are bound to have intersecting axes as well. This means that the contact surface of the cam must be conical, which leads to spherical cam mechanisms. Compared with gear transmissions, cam—roller mechanisms feature low friction, low backlash, and high strength. However, cam mechanisms may end up with a high pressure angle if negative action, a motion in which the cam is driven by mechanism rollers, occurs. This article reports the design of transmissions with spherical multilobe cams (MLCs), as a means to reduce the pressure angle. The kinematics of MLC, including profile generation, undercutting-avoidance, and transmission-quality evaluation, is studied here. A case study has been included, in which the synthesis of a spherical MLC transmission is undertaken as a means to improve the transmission quality of a spherical epicyclic gear train. This train was introduced with the purpose of producing a singularity-free, unlimited-workspace pitch—roll wrist.

The dynamics of parallel Schönflies motion generators: The case of a two-limb system

The formulation of the mathematical model governing the dynamics of parallel Schönflies motion generators (SMGs) is the subject of this paper. These are robotic systems intended to produce motions that entail displacements of the Schönflies subgroup of rigid-body displacements. Such motions are representative of those produced by the serial robots termed SCARA, which involve three independent translations and one rotation about an axis of fixed direction. The main features of SMGs are illustrated with the aid of the McGill Schönflies motion generator. This robot is composed of two limbs, each being a four-joint RΠΠR - R representing a revolute, Π a Π joint, or a parallelogram linkage - kinematic chain, with only two joints actuated. One important feature of the McGill SMG is its mass distribution, as its moving parts account for about 10 per cent of the mass of its drive units, which are (a) fixed to the robot frame and (b) the only steel parts of the whole robot. Moreover, its joints account for roughly 10 per cent of the total mass of its moving parts, fabricated from aluminium, which justifies neglecting the joint inertia in the mathematical model. This feature calls for a formulation of the model in question in terms of the motor displacements, rather than the joint displacements, as the generalized coordinates of the model. Furthermore, in order to derive the model, the robot is decomposed into two subsystems, the drive and the linkage, the drive being decomposed, in turn, into two subsubsystems, the epicyclic gear train and the right-angled gearbox. The robot kinematics is first derived and then the dynamics model is formulated by means of the natural orthogonal complement. In the framework of this methodology, the inertia and what are called the Coriolis matrices of the mathematical model are additive, in the sense that they can be computed as the sum of the contributions of the different subsystems and subsubsystems of a given mechanical system. The contributions of the subsystems and subsubsystems, in turn, can be computed as the sum of the contributions of the individual moving parts of these. Some general results applicable to all SMGs are derived, which leads to the simplification of the mathematical model of such systems.